In the life of a galaxy, col­li­sions don’t al­ways mean de­struc­tion; they can of­ten re­sult in the chaotic birth of some­thing new and beau­ti­ful

Sky at Night Magazine - - CONTENTS -


This ac­tive, glow­ing ob­ject is NGC 4490, a galaxy that is still re­cov­er­ing from a col­li­sion with a smaller galac­tic neigh­bour. It was once a barred spi­ral, prob­a­bly sim­i­lar to the Milky Way, but its shape has been de­formed due to its en­counter with ir­reg­u­lar galaxy NGC 4485, not seen here.

In this Hubble im­age, the most in­tense, de­struc­tive pe­riod of the col­li­sion is al­ready over; the two gal­ax­ies have passed through each other and are speed­ing apart once more. NGC 4490, hav­ing lost its former spi­ral shape, is nick­named the Co­coon Galaxy.

Such col­li­sions don’t sim­ply re­sult in de­struc­tion and dis­tor­tion, how­ever. The sheer force and en­ergy cre­ated in the galac­tic crash is enough to gen­er­ate bursts of star for­ma­tion out of the in­ter­stel­lar dust and gas, seen here as glow­ing pock­ets of red. This red is caused by dense clouds of ionised hy­dro­gen be­ing il­lu­mi­nated by the light of hot, new­born stars. NGC 4490 is clas­si­fied as a star­burst galaxy, which means that stars are form­ing at a rate quicker than the stel­lar in­gre­di­ents can be re­plen­ished.

A thin bridge of stars, not seen in this im­age, con­nects the two gal­ax­ies as they speed away from one an­other. This bridge stretches for more than 24,000 lightyears.

Per­haps our own Galaxy will go through a sim­i­lar event one day. It is thought that our neigh­bour­ing An­dromeda Galaxy will col­lide with the Milky Way in about four bil­lion years, with a po­ten­tially sim­i­lar fall­out to what astronomers have ob­served here.

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